Measuring instrument



MESURIG INSTRUMENT L* Inventor flllorney Feb. 2l, 1933. `K HARTLEY I v1,898,534

MEASURING INSTRUMENT Filed oct. s, 1931 s Sheets-sheet 3 v1 v I N N l?:t: (n

Nv Inventor d .T kN

` ,/lliomey Plantea Feb. 21, i933 UNITED STATES PATENT lol'fllca Nimmmamar, or neueren,

.riassume nrsfrnulrmrr Application med- October 8, 1931. Serial No.566,778.

This invention appertains to new and useful improvements in measuringinstruments and more particularly to an instrument for measuring`small'diierences in the Aforce of gravity.

The principal object of this invention -is to provide a measuringinstrument for measuring small differences in the force of gravit with aprecision of about one-ten thousandt lo of a dyne per gram, which isabout one-ten millionth of the total force.

Previous attem ts to do this have not suc ceeded in tting tter than onepart in one hundred t ousand; chiey because of diili# 5 culties due totemperature effects and to elastic hysteresis.

During the course of the followin specification, other important volectsan advantages of the invention wi readily become 2 ap arent to thereader.

fn the drawings Fi re 1. represents a side elevational view of t einstrument diagrammatically arran ed.

1g. 2 represents avertical sectional view through the scope. H

Fig. 3 represents a vertical sectional view through the beam lookingtoward the weight.

Fig. 4 represents a top plan view of the o base and beam.

Fig. 5 represents a side elevational view of the base and beam.

Fig. 6 represents an end elevational, view 85 of the base looking towardthe mirrors and Referring to the drawings wherein like numeralsdesignate like parts, it canbe seen that a weight 5 suspended from aspring 6 and iexibli connectedto a very light weighing beam in ed at oneend as at 7 by a palr of' phosp or bronze ribbons while its opposite endcarries a pair of small mirrors 8. Li ht from a small electric lamp 9`at the top o the apparatus passes through a lens 10 and is reflectedfrom the mirrors back through the lens to the reflecting prism 11 andthen to the e e piece 12 where an image of theflament o the lamp can beobserved. If the two mirrors 8 are in the same plane,

the two images form a single line of light,

beam adjusting means having ports'omitted.`

is# Russmznto the eyepiece about 600 millimeters so that o themagniication is 1200 for each mirror and the apparent relativemovementofthe two images of the lamp filament is 2400 times the actual vmovementof the beam.

The tension in the main spring 6 is ad. 05 i justed by the screw 6a sothat it does not quite lift the weight to the zeroposition but leaves asmall fraction of the load (about 1/1000) to be carried'by alightauxiliary sprin 13,

which may be referred to as the weig ing spring. l v

The tension lin this spring 13 is controlled by the micrometer screw 14at the top so that .small changes in the gravitational pullcanbefcompensated lfor by altering the tension in the weighing', spring soas to bring the mirrors back into the same plane. This spring 13 .iscalibrated-'so thatthe rea/din of the micrometer dial 15 gives the actuachange in gravitational force in thousandths of a dyne er gram.'

A suitab e locking mechanism not shownin the drawings. holds the wei htaccurately in the zero 'osition between o servations so that the springis kept under constant tension and never relaxes, thus avoiding errorsdue to hysteresis. This mechanism is complex, as j each side. of the sring must be securely held so that jolting wi l not produce an increasedstressin any part. However, such securing 90' I means can taken care ofin nume'rous ways, and need not form part of the present inven- Theeffect of temperature on the spring is compensated for, as far aspossible, by an 95 arrangement of expansion members .i'n the' frame,similar to the old-grid iron, compensated pendulum, and then the wholeinstrument is enclosed in a thermostat which will maintain .thetemperature constant to 10 within 1/100 ofa degree during a whole se- I.

ries of observations. The ordinary labora-- tory thermostat'would not beconvenient for field use but a special type can be devised to accompanythe devicevin the field.

by numeral 16 and which includes the aforementioned lamp 9, prism 11,and eye piece 12,' has the eye piece 12 mounted within the horizontaltube 17 which vcommunicates with the vertical tube 18 at the u er endthereof, at which point the prism 11 and lamp 9 are located.

f It can also be observed, thatthe lamp is provided with a straightfilament, so that the image of the filament to the observer will be astraight line of light.

The tube 18 adjusting screw 6a.' and micrometer screw 14, are carried bythe frame 19 and as is apparent in Fig. 1, it is necessary that someform of bearing block 20 be provided between the micrometer 14, and theweighing spring 13.

' The aforementioned weighing beam which is denoted by numeral 21 isconnected to the frame 19 or some other suitable support by the ribbon22 of phosphor` bronze or other suitable material. As can be clearlyseen in Figs. 4 and 5, the -beam is constructed of alu'- minum or someother suitable light material, so that its weight will be as light aspossible.

Numeral 23 represents phosphor bronze ribbons for connecting the mirrors8 to the beam 21 and stationary supports 24.

Whilev the foregoing specification sets forth the invention in specicterms, it is to be understood that numerous changes in the shape, size,and materials ma be resorted to without departing from t e spirit andscolge of the invention as claimed here' after.

aving thus described my inventio what Iclaimasnewis:- r 1. A measuringinstrument of the character described comprising ar pivoted beam, saidpivoted beam including a weight, a supportlng sprin for the weight, aweighingspring for the am, alight source, and a air A of mirrors on thebeam with which the light source 1s focused, a reflecting medium, and anobservation scope associated with the refilecting medium. y 2. Ameasuring instrument of the character described comprising a pivotedbeam, a

weight attached to the beam and provided wit a spring support, aweighing spring,

Y micrometer screw associated with the weighing springfor controllingthe balance, a light source, mirrors on the beam for reflecting thelight from the light source, and an observation scope concentrated onthe said mirrors.

.3. A measuring instrument of the character' comprising a swingablebeam, ra weight attached to the beam and provided with a spring supporta weighing spring micrometer screwasscated with the Weigh: f

"1,899,534,l y i ing sprin lfor.controlling:the a light source, mgl-forsonthe beam for relectng the lightv from the Llight source an observationt isourcehaving a` single straight 'lilanientfand a'lens for producingimages of the ilamentreileted by the 'said mirrors. 4. 'A'4 measuringinstrument of the character described'comprising a pivoted beam, a weiht attached `to the beam and provided wit va spring support, a weighinspring, micrometer means associated vvlth t e weighing spring forcontrolling the beam, a light source, fmlrrors on the beam for relectmgthe light from the light source, an observascolpejconcentratedon thesaid mirrors, said lig i The observation scope generally referred totion scope concentrated on the said mirrors, 4

a stationary support, each of said mirrors being provided with a strapextending from itself to the beam, and another strap extending fromitself to the stationary support. In testimony whereof I `afiix my siature.

KENNETH HART EY.

